1. Field of the Invention
This invention relates to grinding wheels, and more particularly to a flexible, reusable support fixture for maintaining the green shape of organic bonded abrasive wheels during heat curing processes.
2. Background Information
The grinding wheel art is highly developed and includes a wide range of wheel constructions and wheel fabrication processes adapted to optimize specific grinding operations and/or applications. Abrasive grinding wheels have long been used in the metal working industry to cut and abrade metal. For example, xe2x80x9crough grindingxe2x80x9d wheels are typically used for conditioning operations in which surface defects such as cracks, folds, scale, scabs, seams, cinder patches and burned steel are removed from ingots, blooms, billets and slabs of metal prior to further processing.
The American National Standards Institute (ANSI) has classified various grinding wheel configurations. Examples of these classifications include straight or disc shaped wheels (Type 1), cylinder wheels (Type 2), straight cup (Type 6), flaring cup (Type 11), cone (Type 17) and plug (Type 18), etc.
Grinding wheels are fabricated from abrasive particulates or grains, such as aluminum oxide, silicon carbide, or combinations thereof, of various hardnesses, maintained in a three-dimensional bond matrix. Vitrified bonds are commonly used in precision grinding applications, while organic bonds, such as those provided by phenolic resin, epoxy resin, rubber, shellac or other resin bond material are commonly used in rough grinding applications. These conventional bonded abrasive grinding wheels are commercially available from Norton Company of Worcester, Mass.
Organic bonded abrasive grinding wheels are typically fabricated by conventional hot or cold pressed molding techniques in which a composition or mix of the abrasive and bond material is placed in a mold under pressure to form an uncured or xe2x80x9cgreenxe2x80x9d grinding wheel of predetermined density. This green wheel typically contains a specific amount of air or porosity in addition to the normal abrasive and bond constituents. The green wheel is generally removed from the mold for thermal curing operations. In many cases, especially where the bond or porosity is a high percentage of the grinding wheel, it is necessary to support the periphery both at the peripheral circumference and the circumference of the mounting hole to prevent distortion (slumping or expansive growth) generated by melting of the resin during application of heat in the curing process.
Conventional methods of supporting green wheels include wrapping the wheels in paper and taping and/or inserting the wheel into a bed of sand or similar granular material. These methods are disadvantageously labor intensive and may be environmentally unfriendly due to generation of dust and/or disposal of the paper after removal from the wheel.
Several attempts have been made to eliminate the need for paper or sand beds during curing operations. One approach has been to provide reusable rigid metallic bodies to support the green wheels during curing. This approach, however, has been largely unsuccessful for a variety of reasons, including cost, deformation of the bodies during handling, and dimensional non-compliance. The dimensional non-compliance or improper fit is generated by manufacturing tolerances of both the metallic bodies and green wheels. Such non-compliance is also generated in large part by mold wear, as repeated contact with the abrasive composition tends to wear the mold over time. The green dimensions of the wheel tend to vary according to the degree of tooling wear.
Other approaches have been to cure the green wheel in the mold, rather than remove the wheel prior to cure. Examples of molds generally devised for this purpose are disclosed in U.S. Pat. Nos. 5,275,547 and 2,449,407. A significant drawback of this in-mold curing approach, however, is related to the relatively long cure times, i.e. 12-36 hours, associated with thermally curing grinding wheels, and the relative expense of wheel molds in general. In particular, after the green wheel is formed, the mold remains unavailable for fabricating additional wheels until the thermal curing operation is complete. This lowers the throughput of each mold which tends to increase the effective manufacturing costs of each wheel.
In an attempt to combine the advantages of in-mold and out-of-mold curing, one approach has been to provide rigid mold liners within which the green wheel is molded. The liner and the green wheel disposed therein, are removable from the mold as a unit for curing. An example of this concept is generally disclosed in U.S. Pat. No. 5,645,783. Drawbacks of this approach include increased mold complexity and cost, dimensional variations due to wear between the mold and liner, and deformation of the liner during handling.
Thus, a need exists for an improved support fixture and method for curing grinding wheels and other, similar composites comprising a thermoset polymeric matrix.
According to a first aspect of this invention, a fixture for use in thermally curing an object fabricated from a polymeric matrix, includes a wall portion of predetermined size and shape adapted for supportive engagement with a surface of the object. The wall portion is adapted to maintain the supportive engagement during exposure to a predetermined range of temperatures utilized for thermal curing and is fabricated from a polymeric material that is elastically deformable to facilitate the supportive engagement.
The present invention provides, in a second aspect, a method of forming an object from a polymeric matrix, including the steps of molding the object and providing a support sized and shaped to engage a surface of the object, the support being fabricated from a material that exhibits substantial resilience and resistance to thermal curing temperatures. Subsequent steps include engaging the support with the surface of the object, thermally curing the object, and removing the object from the support.
The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings.